The present invention relates to an internal combustion engine with dual induction system including a primary induction system to direct a first fluid charge into a cylinder to swirl therein under all operating conditions of the engine via a primary intake valve and a secondary induction system to direct a second fluid charge into the cylinder via a secondary intake valve in such a direction as to impede and reduce the swirling motion of the first fluid charge issuing from the primary induction system under predetermined operating conditions of the engine, thereby maintaining the volumetric efficiency of the engine at a sufficiently high level. More particularly, the invention relates to a combustion chamber design of the engine as above.
With conventional internal combustion engines of the construction as mentioned above a primary intake valve and a secondary intake valve are reciprocably supported by a cylinder head, the heads of the primary and secondary intake valves lie within the lower surface of the cylinder head which extends across the cylinder bore when the valves are closed. The entire combustion chamber is formed by the clearance volume between the upper surface of a piston within the cylinder bore and the lower surface of the cylinder head. The secondary intake valve is operated to open in synchronization with the opening of the primary intake valve. Under low and intermediate loads an air fuel mixture charge is drawn into the combustion chamber through a primary induction or primary port passage via the primary intake valve to swirl within the combustion chamber when the primary intake valve is opened. Since the secondary intake valve is opened in synchronization with the opening of the primary intake valve under these loads, the head of the secondary intake valve is likely to hamper the swirling motion of the incoming air fuel mixture from the primary port passage and to cause a portion of the air fuel mixture to flow into a secondary intake port passage. This phenomena will be significant if the primary port passage is angled as to direct air fuel mixture charge to produce a flattened swirl within the combustion chamber.